1. Field of the Invention
The present invention relates to optical communication and more specifically, it relates to a cost-effective wavelength division multiplexer and demultiplexer for use in optical communication. An embodiment of the invention consists of three modules, including a fiber array, a lens array and a filter array/reflector.
2. Description of Related Art
A wavelength division multiplexer (WDM) may be used to combine or separate optical signals having different wavelengths. For example, a two channel WDM can be used to combine two optical signals or to separate an incoming signal into two components that have two different wavelengths.
In optical communications, WDMs have many applications. For example, conventional WDMs are often used for simultaneous transmission of a plurality of optical signals over a single fiber. A conventional WDM may combine the signals having, e.g., wavelengths of 1310 nm and 1550 nm prior to transmission over a single fiber and separate the signals at the receiver.
The cost of providing optical fibers to carry an optical signal between points introduces a large cost in optical communications technology. To reduce this cost, a trend is seen towards carrying more signals on a single fiber rather than providing additional fibers. As a result, the demand for WDMs used to separate or combine such signals has dramatically increased. As the number of signals per fiber increases, the wavelength of each signal becomes closer to the wavelength of neighboring signals. In response to this decrease in spacing between signals, dense WDMs have been developed. Dense WDMs typically separate or combine optical signals having only small differences in wavelength. The difference between wavelengths of neighboring signals in a dense WDM is typically less than 3.2 nm.
In addition to combining and separating closely spaced signals, WDMs must be reliable and perform well in the environment in which they are placed. For example, there are always transmission losses associated with a conventional WDM. These transmission losses should be small and remain constant throughout operation of the WDM. However, the temperature of the environment in which the WDM operates can vary. Thus, a WDM should have a small transmission loss that is relatively insensitive to temperature. A WDM should also be reliable.
Accordingly, what is needed is a system and method for providing a WDM that has improved reliability, is compact and easily manufactured at low cost. The present invention addresses such a need.
It is an object of the present invention to provide a cost-effective wavelength-division multiplexer and/or demultiplexer.
It is another object of the present invention to provide a cost-effective method for fabricating a wavelength-division multiplexer and/or demultiplexer.
It is another object of the invention to provide a cost-effective wavelength-division multiplexer and/or demultiplexer that requires no active alignment or minimum alignment.
The invention is a cost-effective wavelength division multiplexer for use in optical communication. Multiple embodiments are disclosed. One embodiment of the device consists of three modules, including a fiber array, a lens array and a filter array/reflector. Each array is made in wafer level with very precise position control. The three modules are bonded together by conventional wafer bonding techniques that require no active alignment. Each wafer can contain thousands of devices, enabling their manufacture in large quantities at low-cost.
Several advantages are provided by the invention. In addition to eliminating the need for active alignment in the manufacturing process of a wavelength division multiplexer (WDM) transceiver, the invention reduces the footprint of such a device to the order of a few millimeters and the process is suitable for low-cost, large quantity manufacturing.
Although an embodiment is shown which couples four lasers of different wavelength into a fiber, this invention is not limited to the coupling of four lasers, but may be altered to multiplex any desired number of laser wavelength combinations. The whole device consists of three different modules, including a fiber array, lens array and filter array/reflector. The fiber array is connected to the light sources, which optimally are fiber pig-tailed semiconductor lasers. In this way, the light source can be repeatably and accurately placed to the right position in reference to the lens array.
Each fiber is inserted into a separate hole and bonded to the substrate that makes up the fiber array. An alternate to the fiber array formed with a single piece of substrate, two opposing V-grooves may hold the fiber. The input lenses and the output lens on the lens array could be either diffractive or refractive lenses. The input lenses are used to collimate the beams such that light will travel from the lenses at an angle and zigzag between the reflector and the filter array of the filter array/reflector. An output lens is used to focus the beams from each different laser for coupling into a fiber.
The filter array preferably includes edge filters, but may also use narrow-band filters that pass the light of one specific wavelength and reflect the light of the other wavelengths. One embodiment utilizes narrow-band filters having wavelength passbands of about 10 nm. Also, discrete bandpass filters, linear variable bandpass filters, and variable bandpass filters may be used.
The three modules of the invention are built independently. Each light source has to be aligned to its corresponding lens to the accuracy of micrometers. Since the fiber array and lens array are made by standard photolithographic technology, the spacing between elements can be very precisely set (in tens of nanometers). After all the three modules are made, a standard wafer bonding technique is used to bond them to each other. As an alternate approach, one could actively align the fiber optics array to the lens array, to make the positioning between the fiber array and the lens array more accurate prior to bonding. The lens array may be bonded to the filter array/reflector by a variety of techniques. After all the three arrays are bonded to each other, they may be A diced into individual micro optical devices.